1. Field of the Invention
The present invention relates to a diaphragm-type carburetor, and in particular, to an improvement in a diaphragm-type carburetor including a constant-pressure fuel chamber having an outlet bore communicating with a lower end of a fuel nozzle through a fuel jet and a check valve, a fuel pump incorporated in a fuel passage which communicates between an inlet bore in the constant-pressure fuel chamber and a fuel tank for providing fuel for the constant-pressure fuel chamber in response to a pulsation pressure in a pulsation pressure generating source, and a fuel introduction control valve for controlling the introduction of the fuel into the constant-pressure fuel chamber by opening or closing the inlet bore in the constant-pressure fuel chamber. The fuel introduction control valve is provided with a cylindrical valve seat member mounted on an upper wall of the constant-pressure fuel chamber and having the inlet bore in its upper end, and a valve member lifted and lowered within the valve seat member to open and close the inlet bore.
2. Description of the Related Art
A diaphragm-type carburetor is already known, as disclosed, for example, in Japanese Patent Application Laid-Open No. 1-151758.
In such a carburetor, fuel delivered to a constant-pressure fuel chamber by operation of a diaphragm pump is often converted into a large amount of fuel vapor by a pressure pulsation received from the diaphragm pump, heat or vibration received from an engine or the like. When a large amount of fuel vapor is introduced all at one time into the constant-pressure fuel chamber and ejected from the fuel nozzle, the fuel-air ratio of the fuel-air mixture is extremely reduced, thereby causing misoperation of the engine.